Potato (Solanum tuberosum L.) is the world's fourth most important food
crop. Its economical importance arises from its potential to develop tubers, edible
storage organs derived from modified underground lateral shoots, which
accumulate starch. Extensive research has provided evidence that plant hormones
cytokinins have an important role in control of tuberization. Cytokinin
oxidase/dehydrogenase (CKX) is the key enzyme of cytokinin catabolism in
plants, thus transgenic plants expressing CKX genes have provided a valuable
model system for the research of cytokinin homeostasis. Potato (cv. "Désirée")
plants have been transformed with AtCKX1 and AtCKX2 genes from Arabidopsis
thaliana, in order to determine the effects of altered cytokinin homeostasis on the
morphological and physiological features of the transformed potato plants grown
in vitro, with particular emphasis on the tuberization process. A high level of
transgene expression and/or CKX activity in shoots and roots have been
confirmed

in two AtCKX1 and three AtCKX2 lines. The expression of AtCKX genes
has reflected on significant changes in the hormonal homeostasis of the
transformed potato plants grown in vitro, but did not lead to the decrease of total
endogenous cytokinin levels. However in the majority of the AtCKX lines, the
levels of bioactive cytokinins (nucleobases and ribosides), as well as cytokinin
nucleotides, were significantly decreased. In addition, the level of endogenous
indole-3-acetic acid (IAA) was also significantly changed. The altered hormonal
homeostasis reflected on the morphological level, including the tuberization
process. Tuberization was altered in AtCKX potato lines both in long-day conditions, and in continuous darkness...